The word "see" is derived from the Latin sedes, or "seat." In early Christianity, there were five episcopal, or papal, seats that held unique authority in matters of faith and practice throughout the first millennium. These five seats were Rome, Constantinople, Alexandria, Antioch, and Jerusalem. They were collectively known as "The Pentarchy." Eastern Orthodox Christianity retains its commitment to the collective authority of the episcopate of the early Church to this day.
To read more about the 5 Sees, we recommend you start here and keep exploring: https://orthodoxwiki.org/Pentarchy.
We also recommend The Orthodox Church by Timothy Ware.